I was a truck driver, and I still drive solo for long trips in cars. 12-14 hours of driving (in a car) is quite fine all by myself. Key things:

- Start early. Get up around 5, and immediately start driving. Shower, yes; breakfast no. By 10am, you've already done 5 hours or 300+ miles. That will make you feel very good and productive.

- Have brunch at around 10-11, wash up and relax. Total stop time, around an hour. Avoid eating a big lunch late, as that will put you to sleep in the afternoon.

- If you do feel tired in the afternoon, have a short 15-30 minute break. Powernaps are fine.

- Don't stop for dinner until you're done for the day. I'll try to drive till around 7-8pm, find and check-in to motel, and then eat. Go to bed by around 10pm, giving me 7 hours of sleep.

- To save time enroute, try to stop as infrequently as possible. I try to only stop when my gas tank is filled. I'll use the bathroom, I'll buy drinks/snacks, etc, all during that stop. Stopping wastes time.

This way, I can get at least 12 hours on the road, at speed. 800 miles a day is not that hard to do. In fact, having 2 or more drivers are not going to help. I still need that 7 hours in a bed. I still need to eat. More people in the car often simply means more and longer bathroom stops.